The invention relates to a radio-frequency amplifier and more particularly to a plurality of double-ended, grid-controlled electron discharge devices in coaxial-type, radio-frequency cavity-resonator circuits that can be used in television broadcasting, particle accelerators, industrial heating and communications transmitters.
L. S. Nergaard U.S. Pat. No. 2,591,963 on Apr. 8, 1952 discloses a double-ended grid-controlled electron discharge device (triode vacuum tube) and associated coaxial-type, radio-frequency cavity resonators for the input (cathode-grid) and output (grid-anode) circuits. The Nergaard patent discloses a structure having a single electron discharge region. The power handling and high frequency capabilities of grid-controlled tubes are greatly extended by the use of the double-ended configuration instead of the single-ended configuration commonly used in conjunction with large power tubes. As disclosed in Hoover "Advances In The Techniques And Applications Of Very-High-Power Grid-Controlled Tubes", The Proceedings of the Institution of Electrical Engineers, Vol. 105 Part B Suppl. No. 10, 550-558 (1958), a double-ended tube and circuit is, in essence, two single-ended tube-circuit combinations joined at the voltage antinodes of the respective coaxial radio-frequency resonator circuits. The Nergaard patent and the Hoover article are incorporated by reference herein for the purpose of disclosure. A prior art single-ended tube and circuit is shown in FIG. 1. As shown in FIG. 1, the antinode of maximum r.f. standing-wave voltage, V, appears across the tube electrodes at the closed, upper end of the tube, which is outside the electron discharge region of the tube. The electron discharge region, hereinafter called the discharge region, of a tube is the cylindrically disposed portion extending longitudinally along the electron active length of the tube electrodes.
As shown in FIG. 2, a conventional double-ended triode power tube and circuit has an antinode, V, centered within the discharge region for optimum performance. Such a configuration is currently used in super-power tubes and circuits to obtain maximum power, bandwidth, gain and efficiency for ultra-high-frequency operation. As can be seen from FIG. 2, the double-ended triode configuration comprises a cathode, a grid electrode and an anode generally arranged in the form of progressively larger concentric cylinders. The grid electrode contains suitable apertures through which electrons traverse in flowing from the cathode to the anode. A double-ended power tube and cavity-resonator circuit configuration is described in detail in Koros et al. U.S. Pat. No. 2,840,647 on June 24, 1958 and incorporated by reference herein for the purpose of disclosure. The double-ended configuration doubles the length of the discharge region of the tube to permit the generation of at least twice the r.f. power output of a single-ended tube. Typically, the discharge region, extending from V.sub.1 to V.sub.2 in FIG. 2, should not exceed 60 degrees of electrical length at the operating frequency; otherwise, the operational power conversion efficiency of the tube and cavity circuit is degraded because the instantaneous standing-wave of r.f. voltage is progressively lower at both extremities of the triode-electrode region. This fundamental restriction is one of the limitations which determines the maximum theoretical power generating capability of a conventional double-ended tube and cavity circuit. When even greater amounts of r.f. power are required, it is common practice to use special power-combining circuits (e.g. diplexers) to sum the outputs from two or more tube-cavity combinations into a common load. However, the use of such power-combining circuits is disadvantageous from the standpoint of size, power-loss, mechanical-electrical complexity, and cost.
It is therefore desirable to provide a compact and efficient structure for generating large amounts of r.f. power without the use of special power-combining circuits.